Electrochromic devices include an optically active layer disposed between two conductive layers. The two conductive layers are transparent, and during operation, apply voltages to the optically active layer. Such voltages correspond to electric fields passing through the optically active layer. The optically active layer is formed of materials whose light transmittance changes in response to applied electric fields. Thus, each applied voltage induces a transmissive state in the optically active layer. By selectively manipulating the applied voltage, electrochromic devices can switch into a desired transmissive state and regulate light passing therethrough. In general, increased voltages correspond to transmissive states that have a lower transmittance of light.
Electrochromic devices have been integrated into glass panes to produce so-called “smart windows” that selectively regulate light transmission. Within a “smart window,” an electrochromic device spans a functional area of a glass pane, which can be the entirety of the pane. In this configuration, electrical coupling to conductive layers occurs from a perimeter of the glass pane, thereby requiring an electrical charge to move inward when voltages are applied. For this reason, conventional “smart windows” are observed to first darken (or lighten) from their edges to achieve a uniform transmissive state. This darkening (or lightening) then travels inward. Such an effect creates delays when switching between transmissive states.
The delayed switching times can be influenced by sheet resistances associated with the two conductive layers. In operation, electrical charges traveling inward from the perimeter must overcome a cumulative resistance that increases with distance. Thus, during operation, a voltage distribution across the two conductive layers is initially non-uniform, i.e., voltages experienced by the optically active layer can decrease when traveling inward and away from the perimeter. Thus, there is a need for electrochromic devices that reduce sheet resistance effects associated with the conductive layers.